var str = '';

var str2 = null;

if(str.length == 0)
    console.log("empty");


if(str2 === null)
    console.log("null_");

var data_list = [
  {
    website_class_1: '编程',
    website_class_2: '',
    sub_page_title: 'Google C++ 风格指南 ',
    sub_page_num: 1
  },
  {
    website_class_1: '编程',
    website_class_2: 'C++',
    sub_page_title: '字符串库',
    sub_page_num: 2
  }
]

var parent_class_map = new Map();
var child_class_map  = new Map();
for(var i = 0; i < data_list.length; i++){
    if(parent_class_map.has(data_list[i].website_class_1)){
        var sum = parent_class_map.get(data_list[i].website_class_1)
                + data_list[i].sub_page_num;
        parent_class_map.set(data_list[i].website_class_1, sum);
    }
    else
        parent_class_map.set(data_list[i].website_class_1,
                      data_list[i].sub_page_num);
    if(data_list[i].website_class_2 !== '')
        child_class_map.set(data_list[i].website_class_2,
                            data_list[i].sub_page_num);
}

console.log(parent_class_map);
console.log(child_class_map);

if(data_list[0].aa == null)
    console.log('not exist.');


var data_map = new Map();
data_map.set('123', {
    "data1" : 'abc',
    "data2": [],
})

data_map.get('123').data2.push({
    'a1': 100,
    'a2': 200
})
var value = data_map.get('123');
value.data2.push('love');
console.log(value);

const args = process.argv.slice(2);
for(var arg of args){
    console.log(arg);
}
